288 Doccola et al.: Systemic Fungicides Impact on Bluestain Fungi Arboriculture & Urban Forestry 2011. 37(6): 288–292 Impact of Systemic Fungicides on Lesions Formed by Inoculation with the Bluestain Fungus (Ophiostoma minus) in Loblolly Pine (Pinus taeda L.) Joseph J. Doccola, Brian L. Strom, Cavell Brownie, and Kier D. Klepzig Abstract. Ophiostomatoid fungi are important components within the highly damaging insect-fungal complexes attacking trees in North Ameri- ca. This group includes the disease agents responsible for Dutch elm disease and laurel wilt, as well as a number of associates of tree-killing bark beetles. While systemic fungicides have been applied against ophiostomatoids in certain fungus-host systems, the breadth of their utility and their management implications for a wide array of fungus and host species remain uncertain. To evaluate the impact of commercially available fungi- cides against the bluestaining fungus Ophiostoma minus, an associate of the southern pine beetle, researchers conducted two experiments with lob- lolly pines (Pinus taeda; mean dbh 14.2 and 18.5 cm, respectively) in central Louisiana, U.S. The first experiment screened three fungicides (Alamo® Arbotect® , 20-S, and PHOSPHO-jet) for their systemic impacts on O. minus, and the second further evaluated the best performing product (Alamo) alone and in combination with Arbotect 20-S. In all cases, loblolly pines were stem-injected basally and challenged with inoculations of cultured O. minus at time periods ranging from 28 days to 738 days post-treatment. In both experiments, treatment of loblolly pines with Alamo produced the smallest lesion areas, indicating that this treatment was the most effective for limiting the within-tree growth of O. minus. This effect was still present more than two years post-treatment. The study authors conclude that Alamo is the most effective product of those evaluated for prophylac- tic treatment against O. minus, and suggest that evidence is building for the effectiveness of this product generally against ophiostomatoid fungi. Key Words. Dendroctonus frontalis; Scolytidae; Propiconazole; Southern Pine Beetle; Systemic Injection; Vascular Wilt. Insects and disease agents commonly act in concert to cause plant injury. Scolytid bark beetles (Coleoptera: Curculionidae: Scolyti- nae) are frequently associated with fungi that are carried on spe- cialized body structures (mycangia) and/or on the surface of their bodies. Bark beetles attack their host, especially conifers (fam- ily Pinaceae), by boring through the outer bark and construct- ing egg galleries in the inner bark (phloem). During the attack process, vascular tissues of host trees are inoculated with bee- tle-associated fungi and, depending upon the species involved, plant decline and death may be attributable to the beetle, fun- gus, or both. For example, the establishment of the fungus may contribute to host tree mortality by producing toxins, either by mycelial penetration of tissues or by interaction with tree defense responses (Paine et al. 1997). It is a primary goal of pest manage- ment to provide resource protection under all of these scenarios. Systemic fungicides can be effective against bluestain fungi, such as Raffaelea spp. in redbay (Mayfield et. al. 2008), Ophi- ostoma novo-ulmi in American elm (Haugen and Stennes 1999), and Ceratocystis fagacearum in live oak (Wilson and Lester 1995), by reducing lesion formation and favoring tree survival. These organisms cause vascular wilt by occluding the conduc- tive tissues in their host species, often resulting in tree mor- tality. Loblolly pine (Pinus taeda L.) is inoculated with the bluestain fungus Ophiostoma minus (Hedgcock) Sydow & P. Sydow upon attack by the southern pine beetle, Dendroctonus ©2011 International Society of Arboriculture frontalis Zimmermann (Clarke and Nowak 2009). Although the community interactions that occur beneath the bark may be quite complex (involving many species of fungi, mites, and bacteria), the result of a southern pine beetle attack is that the host tree is inoculated with O. minus, which affects tree tissues, the bark beetle colonization process, and ultimately tree death. The role of systemically injected insecticides has been re- cently investigated for efficacy against bark beetles (Grosman and Upton 2006; Grosman et al. 2009; Grosman et al. 2010), but results have varied. Efficacy of emamectin benzoate formulations (Syngenta Crop Protection) was reported against southern pine beetles and ips engraver beetles (Grosman et al. 2009). Adult gal- lery construction, brood development, and emergence were all significantly reduced. However, a number of trees were killed, and because adult beetles tunnel in the phloem before ingesting insec- ticide, the beetles inoculate the tree with various fungi, including bluestains. This leads to uncertainty as to whether mixed treat- ments (fungicides and insecticides) may improve effectiveness. The objective of this study was to evaluate the effectiveness of systemic fungicides for reducing the size of lesions formed in loblolly pine following inoculation with O. minus. Although the bark beetle is believed to be the primary agent of mortality in this system, it is uncertain whether management of the fun- gal associates can assist in tree protection or, at least, minimize the negative effects of bluestain on wood quality. It is also of
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